The diagnostic value of [18F]FAPI-42 PET/CT for pulmonary artery masses: comparison with [18F]FDG PET/CT

Objectives To investigate the potential utility of [F-18]fibroblast activation protein inhibitor (FAPI) positron emission tomography/computed tomography (PET/CT) for evaluating pulmonary artery (PA) masses, and compare it with [F-18] fluorodeoxyglucose (FDG) PET/CT. Methods Participants with clinically suspected PA malignancy were prospectively enrolled and underwent dual-tracer PET/CT ([F-18]FAPI-42 and [F-18]FDG) imaging. Visual analysis and semi-quantitative parameters were compared between the two types of radiotracers. The tissue specimen underwent immunohistochemical staining to verify FAP expression in the tissue. Results Thirty-three patients (18 males/15 females; mean age 53.1 +/- 15.4 years) were enrolled. All 21 patients with malignant PA masses were FDG-positive (100%), whereas 20 out of 21 patients were FAPI-positive (95.2%). All 12 patients with benign PA masses were both negative in FDG and FAPI PET. The mean maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR) of FAPI and FDG in malignant PA masses were significantly higher than those of benign masses. Although there was no significant difference in SUVmax between FDG and FAPI in malignant PA masses (11.36 vs. 9.18, p = 0.175), the TBR (liver) and TBR (left ventricle) were more favorable for FAPI than for FDG (13.04 vs. 5.17, p < 0.001); (median: 7.75 vs. 2.75, p = 0.007). Immunohistochemical analysis (n = 16) validated that the level of FAP expression corresponded strongly to the uptake of FAPI in PET/CT scans (r(s) = 0.712, p = 0.002). For clinical management, FAPI PET found more metastatic lesions than FDG PET in 4 patients, with 2 patients upgrading and 1 patient changing treatment decisions. Conclusions FAPI PET/CT is feasible in the diagnosis of PA masses. Although not superior to FDG PET/CT, FAPI PET/CT showed better target-to-background contrast. Clinical relevance statement This study found that FAPI PET/CT is not superior to FDG PET/CT in diagnosing PA masses, but FAPI PET/CT displays better target-to-background contrast and more positive lesions, which may help improve disease management.